[Bug 106175] amdgpu.dc=1 shows performance issues with Xorg compositors when moving windows

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=106175

--- Comment #45 from rropid at gmail.com ---
(In reply to bmilreu from comment #43)
> If devs want an easy test case, use these links for reproducing it in
> chromium:
> 
> https://www.vsynctester.com/
> https://www.testufo.com/photo
> https://www.slither.io
> 
> move the cursor around, move/resize some windows. you will notice it
> 
> the vsync/cursor stutters and frame-skips are pretty noticeable with dc=1 on
> all three links
> 
> KWin, compton, TearFree, mutter, xfwm4 all have the same problems.

I just tried dc=1 and I only seem to have a problem if I use TearFree. Things
are totally fine without TearFree.

To be clear about what I'm doing here right now:

I made sure DC is enabled:

  $ systool -vm amdgpu | grep dc
      dc                  = "1"
  $ dmesg | grep -i display
  [    1.014297] [drm] Display Core initialized with v3.1.59!

I removed TearFree from my X config:

  $ cat /etc/X11/xorg.conf.d/20-amdgpu.conf 
  Section "OutputClass"
      Identifier "my amdgpu settings"
      MatchDriver "amdgpu"
      Option "DRI" "3"
  EndSection

And I started Compton like this to make sure it's a clean config:

  $ compton --config /dev/null --backend glx --vsync opengl

With this setup, I don't seem to have any stutter. I visited the websites you
mention in a Chromium window, then opened another window and tried moving
things around and resizing. It behaves fine, same as what I know from normally
using dc=0.

Kernel is 4.19.2, Mesa 18.2.4, Xorg 1.20.3, the GPU is a RX480, monitor is 60
Hz.

After I had typed this, I have now added TearFree to the X config and restarted
X:

  $ cat /etc/X11/xorg.conf.d/20-amdgpu.conf 
  Section "OutputClass"
      Identifier "my amdgpu settings"
      MatchDriver "amdgpu"
      Option "TearFree" "true"
      Option "DRI" "3"
  EndSection

Now, with TearFree enabled, things are super terrible. Trying to move a window
around has extreme stutter, it seems to drop frames. If I restart Compton with
"GALLIUM_HUD=fps" and then try moving a window around in circles, I can see it
stays below 40 fps instead of hitting the 60 fps that it should be running at.

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